In the fabrication of flip-chip microelectronic assemblies, it is conventional to use a capillary flow underfill process which involves first making a circuit board by applying a fluxing agent onto a substrate, followed by a placement of flip-chips having solder bumps on the substrate, and subjecting the assembly to a first heating cycle to melt the solder bumps, so as to create operable interconnections between the substrate and the electronic elements in the flip-chips. A circuit board having flip-chips connected to the substrate is thereby formed. An underfill adhesive material is introduced only after the interconnections (or after the circuit board) has been fabricated. This typically involves a further step of applying the underfill adhesive material along the circuit board and allowing the underfill adhesive material to reflow into the spaces between the solder interconnections (i.e., the solder bumps) by capillary forces. The circuit board with the underfill adhesive material disposed thereon is then subjected to a second heating cycle so as to cure the underfill adhesive material, i.e., to cause cross-linked network bonding within the underfill adhesive material domain, but not to cause melting of the solder lest the interconnections formed during the first heating cycle are damaged. As can be seen, in the conventional process of making a flip-chip microelectronic assembly, two heating cycles are required. Since each heating cycle requires time for the temperature to be elevated to a desired level and time for cooling, there is a strong need to increase the efficiency of the flip-chip assembly process in terms of cutting down the production time and reducing the energy consumed.
Thus, there is a need for an improved encapsulant for use in a process of manufacturing flip-chip microelectronic assemblies wherein the time to produce the flip-chip assemblies and/or the energy consumed in the production of the flip-chip assemblies are reduced or minimized. Additionally, there is a need for an improved encapsulant for use in a process of manufacturing flip-chip assemblies wherein only one heating cycle is utilized and wherein a reflow underfill process is used for the arc welding of the circuit board to the substrate.
Further there is a need to develop an improved adhesive material that can be used when arc welding an electronic device and a substrate, wherein the thermal properties (i.e., both the glass transition temperature and thermal expansion coefficient) of the adhesive material are suitable for application of the adhesive material in packaging of electronic products.
U.S. Pat. No. 6,680,436 B2 is directed to the application of a reflow encapsulant to electronic devices and substrates. The reflow encapsulant of U.S. Pat. No. 6,680,436 B2 includes a formulation of a resin having epoxy and flexibilisers, hardener systems comprising epoxides and a cross-link agent, an inorganic additive present at about 8-20% by weight of the formulation, an organic salt catalyst, and a silane coupling agent. The cross-link agent reacts with the resin to form a cross-linked network and also serves as a fluxing agent.
In contrast to U.S. Pat. No. 6,680,436 B2, the present disclosure relates to a reflow encapsulant material that includes an epoxy resin, an anhydride curing compound, a metal acetylacetonate or a metal acetonate catalyst, an inorganic filler that includes alumina nanoparticles, and a fluxing agent having a hydroxyl group such as glycerol. The inventors found that if the fluxing agent of the present disclosure, which is used to flux the oxide on the surface of the solder bumps, was not added to the reflow encapsulant material, the solder bumps would not be reflowed and there would be no attachment between the substrate and flip-chips.
U.S. Pat. No. 6,467,676 B1 is directed to the development of a no-flow underfill encapsulant adhesive that is able to flux the oxide on the surface of solder bumps. The underfill encapsulant adhesive includes an epoxy resin, a curing agent, a catalyst, and a fluxing precursor of the hydroxyl type.
In contrast to U.S. Pat. No. 6,467,676 B1, the present disclosure relates to a reflow encapsulant material that includes alumina nanoparticles as the inorganic filler. The inventors found that if the inorganic filler alumina nanoparticles of the present disclosure were not incorporated in the reflow encapsulant material, the thermal properties of the reflow encapsulant material would not be suitable for application of the reflow encapsulant material. Moreover, when the alumina nanoparticles were incorporated into the reflow encapsulant material, the glass transition temperature of the reflow encapsulant material increased from 134.8° C. to 141.8° C. while the thermal expansion coefficient of the reflow encapsulant material decreased from 91.58 ppm/° C. to 35.68 ppm/° C.
US 2003/0162911 A1 is directed to the development of an underfill encapsulant material to be used in a no-flow encapsulant process. The underfill encapsulant material includes an epoxy resin, a curing agent, a catalyst, and a fluxing agent.
In contrast to US 2003/0162911 A1, the present disclosure relates to a reflow encapsulant material that includes alumina nanoparticles as an inorganic filler. The inventors found that if the inorganic filler alumina nanoparticles of the present disclosure were not incorporated in the reflow encapsulant material, the thermal properties of the reflow encapsulant material would not be suitable for application of the reflow encapsulant material. Moreover, when the alumina nanoparticles were incorporated into the reflow encapsulant material, the glass transition temperature of the reflow encapsulant material increased from 134.8° C. to 141.8° C. while the thermal expansion coefficient of the reflow encapsulant material decreased from 91.58 ppm/° C. to 35.68 ppm/° C.
US 2003/0175521 A1 is directed to arc welding of electronic devices and substrates to be used in flip-chip assemblies and in particular to the development of encapsulant material to be used in the encapsulant process. The adhesive encapsulant material of US 2003/0175521 A1 includes an epoxy resin, and a curing agent that cross-links the epoxy resin and also functions as a fluxing agent.
In contrast to US 2003/0175521 A1, the present disclosure relates to a reflow encapsulant material that includes an epoxy resin, an anhydride curing compound, a fluxing agent having a hydroxyl group such as glycerol, and alumina nanoparticles as an inorganic filler. The inventors found that if the fluxing agent of the present disclosure was not added to the reflow encapsulant material, the solder bumps would not be reflowed and there would be no attachment between the substrate and flip-chips. Further, the inventors found that if the inorganic filler alumina nanoparticles of the present disclosure were not incorporated in the reflow encapsulant material, the thermal properties of the reflow encapsulant material would not be suitable for application of the reflow encapsulant material.
U.S. Pat. No. 6,180,696 B1 is directed to the development of a no-flow underfill epoxy material to be used in a no-flow underfill process. The adhesive material of U.S. Pat. No. 6,180,696 B1 includes an epoxy resin, a curing agent, a catalyst, a fluxing agent, a diluent, a coupling agent, a surfactant, and fumed silica as an inorganic filler.
In contrast to U.S. Pat. No. 6,180,696 B1, the present disclosure relates to a reflow encapsulant material that includes alumina nanoparticles as an inorganic filler. The inventors found that when a silica inorganic filler was incorporated into the reflow encapsulant material in place of the alumina inorganic filler with a similar quantity as was used with alumina, then the thermal properties of the reflow encapsulant material were not suitable for application of the reflow encapsulant. On the other hand, when alumina nanoparticles were incorporated into the reflow encapsulant material, the glass transition temperature of the reflow encapsulant material increased from 119.7° C. to 141.8° C. while the thermal expansion coefficient of the reflow encapsulant material decreased from 51.10 ppm/° C. to 35.68 ppm/° C.
US 2008/0265438 A1 is directed to the development of an epoxy adhesive for use in the assembly of a flip-chip semiconductor device via a no-flow underfill process. The epoxy adhesive of US 2008/0265438 A1 includes an epoxy resin, a curing agent, a silica inorganic additive that can have an average size of about 0.1 to 1.0 micrometer, a desiccant, and a fluxing agent.
In contrast to US 2008/0265438 A1, the present disclosure relates to a reflow encapsulant material that includes an epoxy resin, an anhydride curing compound, a fluxing agent having a hydroxyl group such as glycerol, and alumina nanoparticles as an inorganic filler. The inventors found that when a silica inorganic filler was incorporated into the reflow encapsulant material in place of the alumina inorganic filler in a similar quantity as was used with alumina, then the thermal properties of the reflow encapsulant material were not suitable for application of the reflow encapsulant. On the other hand, when alumina nanoparticles were incorporated into the reflow encapsulant material, the glass transition temperature of the reflow encapsulant material increased from 119.7° C. to 141.8° C. while the thermal expansion coefficient of the reflow encapsulant material decreased from 51.10 ppm/° C. to 35.68 ppm/° C.
U.S. Pat. No. 7,482,201 B2 is directed to the preparation of an electronic article that includes an electronic device that is connected to a substrate via the use of an underfill adhesive, wherein the underfill adhesive is the reaction product of a thermosetting resin, a curing agent, and surface-treated silica nanoparticles. The silica nanoparticles are substantially spherical, non-agglomerated, amorphous, and solid. The silica nanoparticles have an average size of 5 to 600 nanometers and are added in a quantity of 30 to 70% by weight.
In contrast to U.S. Pat. No. 7,482,201 B2, the present disclosure relates to a reflow encapsulant material that includes an epoxy resin, an anhydride curing compound, a fluxing agent having a hydroxyl group such as glycerol, and alumina nanoparticles as an inorganic filler. The inventors found that if a silica nanoparticle inorganic filler was incorporated into the reflow encapsulant material in place of the alumina inorganic filler in a similar quantity as was used with alumina, then the thermal properties of the reflow encapsulant material were not suitable for application of the reflow encapsulant.
US 2005/0181214 A1 is directed to the preparation of an epoxy adhesive that can be cured. The formula of the epoxy adhesive includes an epoxy monomer and/or an epoxy oligomer, a curing agent, and organofunctionalized colloidal silica. The organofunctionalized colloidal silica have an average particle size of about 1 to 250 nanometers and are added in a quantity of about 0.001% to 90% by weight.
In contrast to US 2005/0181214 A1, the present disclosure relates to a reflow encapsulant material that includes an epoxy resin, an anhydride curing compound, a fluxing agent having a hydroxyl group such as glycerol, and alumina nanoparticles as an inorganic filler. The inventors found that if the glycerol fluxing agent was not incorporated into the reflow encapsulant material, then the solder bumps would not be reflowed when connecting the substrate and flip-chips. In addition, the inventors found that if a silica nanoparticle inorganic filler was incorporated into the reflow encapsulant material in place of the alumina inorganic filler in a similar quantity as was used with alumina, then the thermal properties of the reflow encapsulant material were not suitable for application of the reflow encapsulant.